The present invention relates to compositions suitable for use as lubricant additives which contain an ester-substituted hindered phenol antioxidant and other additives suitable for lubricants such as a detergent or a dispersant. The present invention provides an economical antioxidant which has good performance properties when used in lubricant formulations especially for heavy duty diesel engines and passenger car crankcase engines.
Antioxidants are an important class of additives since they are used to provide and/or improve the antioxidation performance of organic compositions, including lubricant compositions that contain organic components, by preventing or retarding oxidative and thermal decomposition. Antioxidants in some applications can result in an increase in volatility which can be undesirable due to required environmental regulations and/or performance standards.
It is known to use a hindered, ester-substituted phenol antioxidant in an oil of lubricating viscosity to reduce oxidation breakdown and improve cleanliness.
U.S. Pat. No. 5,523,007, Kristen et al., Jun. 4, 1996, discloses a lubricant oil composition comprising a diesel engine lubricating oil and, as antioxidant, a compound of the formula
X can be —CH2—CH2—C(═O)—OR and R is a straight chain or branched alkyl radical of the formula —CnH2n+1 wherein n is an integer from 8 to 22.
U.S. Pat. No. 3,285,855, Dexter et al., Nov. 15, 1966, discloses stabilization of organic material with esters containing an alkylhydroxyphenyl group. The ester can have the structure
in which x has a value of from 0 to 6, inclusively, and y has a value of from 6 to 30, inclusively. The “lower alkyl” groups can be t-butyl. Organic materials which can be stabilized include, among many others, lubricating oil of the aliphatic ester type, and mineral oil.
U.S. Pat. No. 5,206,414, Evans et al., Apr. 27, 1993, discloses a process for the preparation of compounds of the general formula
wherein R1 and R2 are identical or different and are hydrogen, C1-C18 alkyl, phenyl, C1-C4 alkyl-substituted phenyl, C7-C9 phenylalkyl, C5-C12 cycloalkyl or C1-C4 alkyl-substituted C5-C12 cycloalkyl, R3 is hydrogen or methyl, m is 0,1,2, or 3 and n is a number from 1 to 4 or 6, and A can be —OR4 where R4 can be C2-C45 alkyl.
U.S. Pat. No. 6,559,105 of Abraham et al. involves lubricant compositions containing ester-substituted hindered phenol antioxidants.
wherein R3 is an alkyl group containing 2 to 6 carbon atoms, and a dispersant or a detergent, is a useful additive package for lubricant compositions.
U.S. Pat. No. 6,787,663, Adams et al., Sep. 7, 2004 discloses a process for the preparation of a hindered ester-substituted phenol and its use in a lubricant composition of the general formula
wherein R3 is an alkyl group containing 2 to 6 carbon atoms.
The present invention involves a low volatility antioxidant that can provide antioxidation performance, volatility performance, deposit performance, or a combination thereof to a lubricant composition, especially a lubricant composition for an internal combustion engine.